Patch

diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rstindex f73ebfe9bfe2..ff6832191577 100644--- a/Documentation/admin-guide/perf-security.rst+++ b/Documentation/admin-guide/perf-security.rst@@ -84,6 +84,40 @@ governed by perf_event_paranoid [2]_ setting:
locking limit is imposed but ignored for unprivileged processes with
CAP_IPC_LOCK capability.
+perf_events/Perf resource control+---------------------------------++perf_events system call API [2]_ allocates file descriptors for every configured+PMU event. Open file descriptors are a per-process accountable *resource* governed+by RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login+shell process. When configuring Perf collection for a long list of events on a+large server system, this limit can be easily hit preventing required monitoring+configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying+content of limits.conf file [12]_ on some systems. Ordinary Perf sampling session+(perf record) requires an amount of open perf_event file descriptors that is not+less than a number of monitored events multiplied by a number of monitored CPUs.++An amount of memory available to user processes for capturing performance monitoring+data is governed by perf_event_mlock_kb [2]_ setting. This perf_event specific+*resource* setting defines overall per-cpu limits of memory allowed for mapping+by the user processes to execute performance monitoring. The setting essentially+extends RLIMIT_MEMLOCK [11]_ limit but only for memory regions mapped specially+for capturing monitored performance events and related data.++For example, if a machine has eight cores and perf_event_mlock_kb limit is set+to 516 KiB then a user process is provided with 516 KiB * 8 = 4128 KiB of memory+above RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular+this means that if the user wants to start two or more performance monitoring+processes, it is required to manually distribute available 4128 KiB between the+monitoring processes, for example, using --mmap-pages Perf record mode option.+Otherwise, the first started performance monitoring process allocates all available+4128 KiB and the other processes will fail to proceed due to the lack of memory.++RLIMIT_MEMLOCK and perf_event_mlock_kb *resource* constraints are ignored for+processes with CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users+can be provided with memory above the constraints for perf_events/Perf performance+monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability.+
Bibliography
------------
@@ -94,4 +128,6 @@ Bibliography
.. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_
.. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_
.. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_
+.. [11] `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_+.. [12] `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_